1. Field of the Invention
The present invention relates to a system and method for controlling a vehicle speed of an automotive vehicle to follow a preceding vehicle moving on the same traffic lane as the vehicle, wherein an intervehicle distance to the preceding vehicle is measured and the vehicle speed is so controlled that the vehicle automatically follows the preceding vehicle at a safe intervehicle distance on the basis of the measured intervehicle distance and current vehicle speed.
2. Description of the Prior Art
Recently, automatic cruising control systems have been installed on some vehicles to move the vehicles at constant set vehicle speeds. In addition, various automatic vehicle speed control systems associated with the cruising control systems have been proposed in which a distance from the vehicle to a moving object such as another vehicle (hereinafter referred to as an intervehicle distance) which is moving in front of the vehicle is measured and a vehicle speed is so controlled on the basis of the measured intervehicle distance as to automatically follow the other vehicle at a safe intervehicle distance in order to prevent collision on the preceding vehicle and thus improving driving comfortability.
Such systems as described above are exemplified by Janpanese Patent Application Unexamined Open No. Sho 55-86,000 published on June 28, 1980.
In the above-identified document, the system measures the intervehicle distance to the other vehicle which is moving in front of the vehicle and controls the vehicle speed on the basis of the measured result.
Hence, to achieve an appropriate vehicle speed control it is necessary to detect accurately the presence of the other vehicle moving in front of the vehicle on the same traffic lane as the vehicle (hereinafter referred to as a preceding vehicle).
In the system disclosed in the above-identified document, a radar unit is used as means for monitoring the presence of the preceding vehicle and measuring the intervehicle distance to the preceding vehicle.
However, since an electromagnetic wave used as a measuring medium of the radar unit has a high linear directivity, a detection area of the radar unit is limited substantially in a narrow forward movement direction of the vehicle. Hence, if the vehicle is moved on a curved road having a certain radius of curvature, the radar unit may erroneously recognize the presence of another vehicle moving on an adjacent traffic lane to the lane on which the vehicle moves as the preceding vehicle moving on the same traffic lane. Consequently, the appropriate control of the vehicle speed cannot be achieved due to an erroneous control based on an incorrect measured result of the intervehicle distance.